Exemplary embodiments relate to a nonvolatile memory device and a program method thereof and, more particularly, to a nonvolatile memory device and a program method thereof, which are capable of prohibiting a shift in the threshold voltage of an erase cell.
In nonvolatile memory devices which enable electrical program and erasure of data without the refresh function of rewriting data at specific intervals, the interval between neighboring memory cells narrows with an increase in the degree of integration.
FIGS. 1A and 1B are diagrams illustrating the influence on program cells and erase cells due to the interference between neighboring memory cells.
As shown in FIGS. 1A and 1B, a program cell is subjected to a coupling effect from neighboring memory cells that are simultaneously being programmed, whereas an erase cell is subjected to a coupling effect due to all neighboring memory cells regardless of whether they are simultaneously erased. Accordingly, a threshold voltage of the erase cell may be more widely distributed than that of the program cell.
FIG. 2 shows a shift in the threshold voltage distribution of an erase cell.
As shown in FIG. 2, the threshold voltage distribution of an erase cell is shifted due to the program operation for neighboring memory cells. For example, in the case where all memory cells adjacent to an erase cell are programmed with a third threshold voltage distribution C, the erase cell may experience the greatest shift in the threshold voltage distribution. Accordingly, at the time of a read operation, the erase cell may be erroneously read as if it has the threshold voltage distribution of a program cell, for example, a first threshold voltage distribution A.